What is the difference between "Damage Health" and "Ravage Health"?

I've been experimenting with Alchemy in Skyrim, and I've noticed that I've acquired two distinct alchemical effects: "Damage Health" and "Ravage Health". They both cause instant poison damage, so what's the difference? Why do some ingredients give "Damage Health" while others give "Ravage Health instead?"

Ravage Health reduces your maximum HP. Damage Health deals damage.

You can test the effects on yourself with the following potions:

• Red Mountain Flower + Void Salts (Fortify Stamina + Damage Health)
• Eye of Saber Cat + Silverside Perch (Restore Stamina + Ravage Health)

I just tested it myself by combining a harmful effect with a good effect, allowing me to drink the poison. Ravage does not decrease maximum, but rather is a very, very strong DoT effect that lasts 10 seconds. I took something that ravaged magicka by 12 points, and I soon lost half my total mana as the timer counted down - I had 194 total mana. This effect wore off after 10 seconds and the good effects of the potion continued working. My maximum did not seem affected.